This invention relates to an apparatus for the continuous casting of metal products.
Many of the defects occurring on the surfaces of continuously cast metal products consist of cracks in the primary solidifying crust and are due to natural shrinkage of the metal crust during cooling. Other factors causing such defects are too much friction between the crust and the chilling wall as well as the internal static pressure of the metal acting on the crust, such as typically occurs in casting into both open and closed molds. The crust can fracture in all directions in which shrinkage is impeded, unless the elasticity of the material at the correspondingly elevated temperatures is sufficient to completely prevent such cracks from occurring. However, this cannot be expected in the majority of cases.
Problems with surface defects especially arise in the casting of thin layers on rotating cooled cylinders and belts or the like, as is known in the prior art, although the internal static pressure of the metal on the solidifying crust is usually of secondary importance. For these reasons the required widthwise extension of thin layers plays a dominant role. The amount of shrinkage depends on the width which the cast product is to have. Although a lubricant may be introduced between the solidifying crust and the cooling surface, it is technically expensive and there is no assurance that the layer will shrink without fractures occurring transverse or parallel to the casting direction. In the majority of cases any weak area is adequately sealed by the cooling surface which accompanies the layer in its movement until it has completely solidified to prevent the melt from breaking through. However, surface defects such as cracks lead to rejects since there can obviously be no possibility of removing such defects by chiseling or grinding.
Swiss Patent No. 604,970 discloses a process in which the spreading cf the melt on a shaping wall, i.e., a cooling wall, is controlled by the use of electromagnetic forces. However, this process is used exclusively to prevent the metal from penetrating the gap between the fixed side walls and the mold wall during the casting of metal strips.
All known continuous casting processes in which thin layers are cast onto rotating cooling surfaces, share the feature where mechanical boundary elements are missing that the wetting of the cooling surface by the metal has a natural boundary line extending transverse to the casting direction and produced by gravity. The natural boundary line at the same time is the beginning of the solidification extending in the casting direction.